1. Field of the Invention
The present invention relates to a secondary battery, and more specifically, to a secondary battery with a relative position between an electrode tap positioned at an outer circumferential portion of an electrode assembly formed as a jelly roll and a can receiving the electrode assembly jelly roll.
2. Description of the Related Art
A secondary battery is formed by receiving an electrode assembly in a can made of aluminum or aluminum alloy, for example, injecting an electrolyte into the can, and then hermetically sealing the can. In the secondary battery, the electrode assembly includes a positive electrode plate, a separator, and a negative electrode plate. An electrode terminal electrically separated from the can is provided at a top of the battery, so the electrode terminal can function as a positive electrode or a negative electrode of the battery. At that time, the can itself can function as a negative electrode, when the electrode terminal functions as the positive electrode, and function as a positive electrode when the electrode terminal functions as the negative electrode.
The hermetically sealed battery is provided along with safety devices such as a Positive Temperature Coefficient (PTC) element, a thermal fuse, a protective circuit board, e.g., a protecting circuit module (PCM), etc. These safety devices are electrically connected to the positive and negative electrodes of the battery and intercept a current when a voltage of the battery is rapidly raised due to an increase in temperature or excessive charge and discharge of the battery, thereby preventing the battery from being destroyed, for example. The battery provided with the safety devices is typically placed in a packing case to form a battery pack.
FIG. 1 is a partial perspective view illustrating a conventional secondary battery with an electrode tap positioned at a long side portion of the can. The open end of the can 11 is provided with an opening portion 11a, with the electrode assembly 12 being placed in the can 11 through the opening portion 11a, as illustrated in FIG. 1. The electrode assembly 12 is wound up in a jelly roll shape, after the positive electrode plate and the negative electrode plate are stacked therein, along with the separator therebetween. An electrode tap 14 and electrode tap 13, respectively, electrically connected to one of the positive electrode plate and the negative electrode plate, are drawn out from a top of the electrode assembly 12. The electrode tap 13 may be a negative electrode tap and electrode tap 14 may be a positive electrode tap, or electrode tap 13 may be the positive electrode tap and electrode tap 14 may be the negative electrode tap.
The can 11 has substantially a rectangular parallelepiped shape, and is made of metal material, so that the can 11 can function as a terminal.
When the electrode tap (positive or negative electrode tap), coupled to a half or more of a width of the electrode assembly, is positioned at an outer circumferential portion of the electrode assembly jelly roll, the following problems have been noticed. First, even before using the battery, a pressure is applied between the can 11 and a portion of the electrode assembly 12, in the area of the electrode tap 14, due to the close arrangement between the electrode assembly 12 and the can 11, such that the operational ability of the electrode assembly 12 deteriorates.
Further, during use of the battery, the battery cycles between volume expansion and volume contraction, with these expansions and contractions allowing the electrode tap 14 to be pressed between the can 11 and a corresponding electrode plate (the positive electrode plate, the negative electrode plate, or the separator, depending on whether electrode tap 14 is the positive or negative electrode tap), thereby deforming the corresponding electrode plate along a shape of the electrode tap 14. During use of the battery, the deformed portion of the corresponding electrode plate changes to a non-reaction portion due to the pressing, with lithium ions agglomerating around the deformed portion or the peripheries thereof, thereby causing problems such as dendritic deformations, increasing in thickness, etc. These are serious problems when they occur in a high-capacity battery having such a polygonal section.